The invention relates to a regulating member for controlling an intensification of pressure of fuel for a fuel injector.
In the supply of fuel to internal combustion engines, increasing use is made of injection systems which operate at very high injection pressures. Particularly where diesel engines are concerned, which are employed in the TRK sector. It has been found advantageous, in this context, to have accumulator injection systems which generate these high injection pressures by pressure intensification. One example of a fuel injector with pressure intensification is disclosed in U.S. Pat. No. 5,682,858. In this system, a pressure intensifier is arranged in the fuel injector, with a moveable piston which subdivides the pressure intensifier into a low-pressure-side control space and a high-pressure-side working space. The high-pressure-side working space of the pressure intensifier is connected to a fuel line in a fuel injector upstream of an injection nozzle. The low-pressure-side control space is connected to a pressure accumulator via an electromagnetically actuated regulating member formed in the fuel injector which is designed in such a way that, in the initial state, when it is not live, the regulating member breaks the flow connection between the pressure accumulator and the low-pressure-side control space of the pressure intensifier and keeps the control space pressureless. In this operating state, the working space of the pressure intensifier is filled with fuel via the fuel line.
By applying a current to the regulating member it is then switched in such a way that the flow connection between the pressure accumulator and the low-pressure-side control space of the pressure intensifier is opened and the piston in the pressure intensifier is acted upon on the control-space side by the pressure in the pressure accumulator. At the same time, the pressure which is established in the control space, being intensified by a multiple by the piston in the pressure intensifier, is transmitted to the fuel located in the working space of the pressure intensifier. Thereby the fuel, put under high pressure in the working space, has the effect, due to a connection between the working space and the injection nozzle, that the injection nozzle opens and fuel is injected into a combustion space of an internal combustion engine. As soon as the application of current to the regulating member is terminated, the regulating member returns to its initial state, with the result that the flow connection between the pressure accumulator and the control space is broken. The pressure on the fuel in the working space of the pressure intensifier then falls abruptly, the injection nozzle closes and injection is terminated.
In the accumulator injection system with pressure intensification, described in U.S. Pat. No. 5,682,858 A, therefore, the injected fuel quantity is determined by the time window for activating the actuator and by the design of the injection nozzle, that is to say by the fuel quantity injected per unit of time by the injection nozzle. Unavoidable manufacturing tolerances at the injection nozzle consequently result in the injected fuel quantity varying from fuel injector to fuel injector, which, particularly in the case of multicylinder engines, may lead to an uneven behavior of the engine, and in particular to true-running faults. Furthermore, in the known accumulator injector system with pressure intensification, the end of fuel injection into the combustion chamber and consequently the combustion profile depend on the accurate activation of the regulating member. Switching delays occurring during the activation of the regulating member may cause an undesirable lengthening of the injection time, which may be detrimental to the combustion values. Moreover, the regulating member illustrated in U.S. Pat. No. 5,682,858 A has a complicated construction, and consequently results in a high manufacturing outlay.
The object of the present invention is, therefore, to design a regulating member for controlling an intensification of pressure of fuel for a fuel injector in such a way that a simple and reliable regulating function is ensured and, in particular, wide spreads in the injection behavior of the fuel injectors are avoided.
The regulating member according to the present invention is arranged in a fuel injector, in a pressure line which connects a low-pressure-side control space of a pressure intensifier in the fuel injector to a pressure supply, and has an actuator, a valve chamber and a spring-loaded valve piston arranged moveably in the valve chamber. The valve piston, in its position of rest in which it is not actuated by the actuator, makes a flow connection through the valve chamber between an inflow orifice connected to the pressure supply and a first outflow orifice which is connected to the control space of the pressure intensifier. The switching position is brought about by the actuator with the valve piston in a position in which a flow connection is made through the valve chamber between the first outflow orifice, which is connected to the control space in the pressure intensifier, and a second outflow orifice which is kept pressureless.
In the regulating member according to the present invention, activation of the valve piston in the regulating member is necessary only for the start of injection by an injection nozzle in the fuel injector. However, the injection operation of the injection nozzle is terminated automatically, as soon as the entire fuel stored in a working space of the pressure intensifier is injected. The switching times in the regulating member therefore have no influence on the time at which injection is terminated. In the design of the regulating member according to the present invention, the automatic end of injection ensures a high degree of inherent safety in the event of possible operating faults of the regulating member. Moreover, the injection quantity is determined only by the fuel sucked in the combustion space of the pressure intensifier. Manufacturing tolerances of the injection nozzle in the fuel injector therefore have no influence on the metering of the injection quantity.
According to a preferred embodiment of the invention, the regulating member has two conically designed valve seats, on which the valve piston alternatively lies with one of its two conically designed sealing surfaces, depending on the switching state. This design of the regulating member with conical valve seats allows for simple manufacture and, furthermore, a high operating reliability of the regulating member.
According to a further preferred embodiment, the actuator is activated piezoelectrically, which result in high switching speeds, and therefore an improved efficiency of the regulating member.